Steels and method of processing same



Ute Stes Pater 3 001 897 STEELS AND Mnrnoi) 6F PROCESSING SAMIE ElliotS. Nachtman, Park Forest, 111., assignor to La Salie Steel Company,Hammond, Ind., a corporation of Delaware No Drawing. Filed Oct. 22,1956, Ser. No. 617,270 11 Claims. (Cl. 148-12) This invention relates toa new and novel cold finishing method for producing steels havingimproved physical and mechanical properties.

It is an object of this invention to produce and to provide a method forproducting steels having improved physical and mechanical properties,and it is a related object to provide a method of processing steels in acold finishing operation to improve the physical and mechanicalproperties of the steel.

More specifically, it is an object of this invention to provide a methodapplicable to steels of the nonaustenitic type or which strain hardenand which harden by some mode of precipitation during working atelevated temperature to improve the mechanical and physical propertiesof the steel in the cold finishing of such steels, and it is a relatedobject to produce steels having new and improved physical and mechanicalproperties.

This application is an improvement of the copending applications SerialNo. 518,411, Serial No. l8,412,'Serial No. 518,413 and Serial No.518,414, filed June 27, 1955, now Patents No. 2,767,837, No. 2,767,835,No. 2,767,836, and No. 2,767,838, respectively.

In the aforementioned copending applications, description is made of anew and improved method for use in the cold finishing of steels whereinthe steel in the form of a bar, red, tube or wire is worked, as by meansof extrusion or drawing, to eifect reduction in cross-sectional area byadvancing the steel througha die while at a temperature in excess of 200F. but below the lower critical temperature for the steel composition.Depending upon the temperature of the steel being worked, or upon itschemistry or upon the percent reduction taken, various properties, bothphysical and mechanical, can be beneficially infiuenced to produce awide range of values in the steel.

In accordance with the teachings of the aforementioned copendingapplications, improvements in tensile strength, yield strength,machineability, hardness, ductility and other physical and mechanicalproperties of the steel are secured, although some of these propertiesare maximized in certain temperature ranges as compared to others. Forexample, as defined in applications Serial No. 518,411 and Serial No.518,413, improvements in machineability and in mechanical propertiessuch as tensile strength, yield strength, proportional limits, impactstrength and hardness, and physical properties such as surfaceroughness, are secured by advancing the steel through a die to eflectreduction in cross-sectional area while the steel is in a temperaturerange between 450 and 850 F. Within this range, machineability, tensilestrength, proportional limits and yield strengths are maximized when thesteel is drawn while at a temperature within the range of 450- 600 F.Improvements in plastic properties, as represented by elongation andimpact strength, are more noticeable when the steel is advanced throughthe die While at a temperature within the range of 600-850 F.

In addition to the improvement in mechanical and physical properties ofsteel, the processes described in the aforementioned copendingapplications can be employed Patented Sept. 26, 1961 to control theresidual stresses available in the steel to tailor the steel for certainapplications. For example, in the aforementioned copending applicationSerial No. 518,- 412, the development of residual stresses in steel canbe minimized and the type or magnitude of the residual stresses in steelcan be controlled to reduce warpage values and to reduce the developmentof cracks in products fabricated of such steels by advancing the steelthrough a die to effect reduction in cross-sectional area while thesteel is at a temperature in excess of 650 F. and preferably at atemperature within the range of 850 F. to the lower critical temperaturefor the steel composition.

The marked reduction in warpage values which occurs when the steel isadvanced through a die to eiiect re duction in cross-sectional area at atemperature above 650 F. and preferably above 850 F. permits theproduction of steel products having improved physical and mechanicalproperties with the residual stress values as low or lower than valueswhich have heretofore resulted from processing subsequent to drawing, asby heat treatment. High compression stresses, instead of tensilestresses, can be formed in the outer portions of the steel if the steelis advanced through the die to elfect reduction in cross-sectional areaat a temperature in excess of 800- 850 F. followed almost immediately byrapid cooling, as by quenching, for example, in water or oil. Such highcompressive stresses in the surface portions of the steel are extremelyadvantageous in'increasing the torsional fatigue value of the steel atany particular strength value.

Thus, it has become possible, in accordance with the teachings of theaforementioned copending applications, to produce steels havingproperties tailor-made for particular uses by the proper selection ofthe steel from the standpoint of chemistry, by proper selection of theamount of reduction, and by proper selection of the temperature of thesteel advanced through the die to effect reduction in cross-sectionalarea.

It has now been found, in accordance with the practice of thisinvention, that, by a new combination of steps which makes use of thecold reduction step prior to the reduction step at elevated temperature,as described in the aforementioned copending applications, still furtheror other improvements can be secured. In some instances greateruniformity of properties from heat to heat can be produced. A widerrange of properties can be made available with a given chemistry andsome of the physical and mechanical properties of the steel can be stillfurther increased. The improvement which makes use of a cold reductionstep in advance of the passage of the steel through a die at elevatedtemperature to effect a reduction in cross-sectional area is somewhatindependent of the amount of reduction that is taken in the earlier coldreduction step, but the degree of improvement, especially in the tensileand yield strength properties of the steel, is somewhat proportional tothe amount of reduction that is taken in the cold reduction step. Forexample, the tensile strength properties and the yield strengthproperties of the steel, as well as the proportional limits, aremaximized by advancing the steel through a die to take a heavy reductionas compared to a light reduction at room temperature prior'toadvancement of the steel through a. die to take a subsequent reductionwhile the steel is' at elevated temperature.

The improvement in physical and mechanical properties securedby thecombination of steps described is available when, in the subsequentelevated reduction step, the

steel is advanced through the die to eifect reduction in cross-sectionalarea while at a temperature within the range of 200 F. up to the lowercritical temperature for the steel composition, as in the aforementionedcopending applications, but the improvements are maximized, especiallyin tensile strength and yield strength, when the temperature at whichthe steel is advanced through the die in the subsequent elevatedreduction step is in the range of 450-850 F. and preferably within therange of 500-750 F. -While. subsequent processing, as by slow cooling inair or by rapid cooling as by means of a water quench or oil quench hassome effect on the stresses developed in the processed steel and on someof the mechanical and physical properties, such subsequent cooling doesnot materially affect the improvements in the physical and mechanicalproperties developed by the combination of cold reduction with reductionat elevated temperature.

Steels capable of use in the practice of this invention arecharacterized by the ability to strain harden and harden by some mode ofprecipitation or other rearrangement when worked at elevated temperaturewithin the ranges described, as by drawing or extrusion or rolling toeffect reduction in cross-sectional area. Thus steels which may beemployed in the practice of this invention can be distinguished overother steels, such as the hard-to-draw high-speed steels or carbon toolsteels of the types described in the Kronwall Patent No. 2,400,866.

Advancement through a die to effect reduction in crosssectional area isintended to include the advancement of the steel through a draw die in adrawing operation to effect reduction in cross-sectional area. Itincludes the advancement of the steel through an extrusion or roller dieto effect reduction in cross-sectional area. While not equivalent fromthe process standpoint, many of the properties described have been foundcapable of being developed when the described steels are processed byother processes for reduction in cross-sectional area, such as in arolling process.

As used herein, the term percent reduction is meant to relate to thetrue reduction as represented by the formula D D D where D is theoriginal hot roll diameter of the steel, D is the final diameter of thesteel.

Most of the terms herein employed are well known to the art. Thefollowing will define some of the lesser known terms or terms upon whicha special meaning is placed, and the following will also define some ofthe abbreviations which will hereinafter be employed in the morespecific illustration of this invention.

The term proportional limi corresponds to the point in the stress-straincurve where the greatest stress that the material is capable ofsustaining without deviation from the law of proportionality of stressto strain occurs (Hookes law). This point is of particular importance insteel and, in practically every instance, is measurably increased toheretofore unobtainable high values when the steels of thenon-austenitic type are produced, as by drawing or extrusion at elevatedtemperatures within the range defined in the aforementioned copendingapplications.

Residual stress is related to the warpage values secured in the finishedsteel. The warpage value is an indication of the concentration andcharacter of the longitudinal stresses present in the steel. Theresidual stress is obtained by means of a warpage test whereby thelength of the test piece is determined as being five times the diameterplus 2 inches. The test pieces are slotted through a diameter for adistance five times the diameter. The length of the slot is recorded andthe maximum diameter perpendicular to the slot is also recorded. Thedifferences between the diameter before slotting and after slottingcomprise the flare caused by the presence of residual stresses. Theflare is considered positive, indicating tensile stresses in the outerarea of the material, if the bar expands on slotting. The flare isconsidered negative, indicating compressive stresses in the outer areaof the material, if the ends move towards the cut which is made throughthe diameter. The warpage values determined for evaluation arecalculated with the following equation:

(Ls), X100 Warpage factor:

where The pull load is determined by recording the average hydraulicpressure reading of the chain drag at idling speed and while drawing thebar stock at the rate of 25 feet per minute on a 30,000 poundWaterbury-Farrell hydraulic draw bench. The corrected hydraulic pressurereading of the drawing load minus chain drag was converted to poundspull by multiplying by a factor of 22.9. The factor 22.9 was obtainedfrom the slope of a calibration curve of Waterbury-Farrell hydraulicpressure versus Tinius-Olson tensile testing machine pound pull.

Where Izod impact is mentioned, the values in foot pounds was obtainedby averaging the impact results from three equidistant 45 degree notches(0.130 deep) at F. on a 0.45" diameter round it 4 /2 long specimen.

As used herein, the term hardness corresponds to the Diamond PyramidNumber (DPN) or Vickers Hardness measured on a Gries Reflex hardnesstesting machine employing 136 Pyramid Diamond at a 50 kg. load.

The abbreviations used in the following tables are as follows:

ETD (A)=elevated temperature drawing with air cooling after drawingETD(W) or (0) =elevated temperature drawing with a water quench or anoil quench after the final drawing operation L =light reduction at roomtemperature H =a moderate to heavy reduction at room temperature Theconcepts of this invention will hereinafter be illustrated with foursteels taken as representative of the class of steels which may beemployed. These representative steels will hereinafter be referred to asC-1018, C-1 144, C-1080 and 4140. The following is a ladle analyses ofthese steels in which the major ingredients other than iron are setforth:

Chemistry 5 5 Grade 0 Mn 1? S 81 Or Mo G1018. 18 .88 015 037 C-1l4445 1. 51 018 28 .22 O1080 86 79 010 031 20 0 4140 43 .88 018 020 26 .8618 The procedure for processing the steels in the development of thedata set forth for the support of the invention is as follows:

(A) HOT ROLLED PREPARATION The data was developed on hot rolled barstock of the following dimension:

The hot rolled bar stock as received was descaled by pickling insulphuric acid and limed to prevent rusting.

5 HEATING PROCEDURE FOR THE ELEVATED DRAWING STEPS All of the bars,except those cold drawn at room temperature, were heated to the desiredtemperatures in a gas-fired furnace and the bars were lubricated priorto drawing.

(C) DRAFTING PRACTICE The cold reduction steps were carried out byadvancing the steel bar through a draw die to effect the desiredreduction in cross-sectional area while the steel was at roomtemperature. Reduction at elevated temperature was carried out byadvancing the steel bars through the draw die to effect the desiredreduction in cross-sectional area While the steel was at a desiredelevated temperature.

The data in the following tables sets forth the physical and mechanicalproperties of the hot rolled steels; the same steels drawn at roomtemperature; the same steels drawn at elevated temperature (ETD) asdescribed and claimed in the aforementioned copending applications; thesame steels in which a light reduction was taken at room temperatureprior to reduction at elevated temperature (L +ETD); and the same steelsin which a heavy reduction was taken at room temperature prior toreduction at elevated temperature (H -PET D). The last two represent theimproved practice of this invention. In the development of the data, thesame steels of the same composition were employed in the various tests.The amount of reduction was held as nearly the same as possible and thedata set forth was from a comparable temperature range, as indicated ineach of the tables.

The data set forth in the following tables is not intended to provide acomparison for distinguishing the instant invention over the inventiondescribed and claimed in the aforementioned copending applications,although some of the data will indicate the development of improvementsin some properties over the properties developed in the same steel byreduction at elevated temperature. It should be understood that thecombination of steps which combines a cold reduction step in advance ofa reduction at elevated temperature permits the development of certainproperties in steel incapable of being secured by conventional methodsof cold finishing steel or, in some instances, even by reduction atelevated temperature.

TABLE I -1018 STEEL Loo 8% Hon Hot roll CD ETD +ETD 31%+ 26% 18% ETDTensile strength, p.s.i. 68, 375 98, 500 109,750 120, 750 128,000 Yieldstrength, psi. 46, 875 97, 500 107, 500 116,500 122,000 Elongation,percent. 36.0 14. 12. 13.0 12. 5 s 13, 168 11, 450 9, 733 7, 443 Izodimpact, ft lbs 87.0 9. 3.7 2.7 7.0 Hardness, DPN.-. 151 220 249 271 266Warpage factor 021 331 264 472 623 TABLE II 0-1018 STEEL Lap 8% Hon Hotroll OD ETD +ETD 31%+ 26% 18% ETD 98, 000 109,250 112, 500 128,750 97,500 107, 500 108, 750 122, 500 12. 5 9. 5 13.0 11.5 13, 168 11, 450 9,733 7, 443 12.0 3.0 3. 7 4.0 216 249 245 266 Warpage factor 319 288 399566 CD=0old drawn at room temperature. ETD=Drawn at 650700 F.

Table I=Results air cooled.

Table II=Results water or oil quench.

TABLE III 0-1144 STEEL Loo Hen Hot roll OD ETD 4.5 21.5%

22% 22% +ETD +ETD 17.5% 15.5%

Tensilestrength, p.s.i-.. 108,000 132,750 150, 250 152,000 172, 500Yield strength, p.s.i 70, 500 118,750 145, 000 146, 000 172,500Elongation, percent 23.0 13.0 9. 5 8. .6. 0 11, 450 9, 8, 588 9, 733 18.0 4. 0 4. 4. 7 266 318 301 356 Warpage factor 732 661 803 008 TABLE IVLon Hon Hot roll OD ETD 4.5% 21.5%

22% 22% +ETD +ETD Tensile strength, p.s 1 108,000 133,000 152, 250 155,000 172, 500 Yield strength, p.s. 70, 500 127, 500 147, 500 150,000 172,500 Elongation, percent 23.0 9. 8. 7. 6.0 s 11,450 9,160 8, 588 9, 733Izod impact ft lb 32. 7 22. 3 3. 4. 0 4. 0 Hardness, DPN- 220 258 324307 336 Warpage factor- 004 789 639 782 031 OD=Cold Drawn roomtemperature. ETD=Drawn at 600-650" F. Table III= Results air cooled.Table IV=Results water or 011 quench.

TABLE V C1080 Steel Leo Hon Hot CD ETD 5.5% 22% Roll 22% 22% +ETD +ETDTensile strength, p.s.i. 144, 500 168, 250 180, 000 170, 250 183, 000Yield strength, p.s i 76, 000 136. 000 154, 500 140, 000 140, 000Elongation, percen 12. 2. 3. 9. 3. 6 Pull, lbs -1 16, 603 11, 450 12,595 7, 443 Izod impact, It. 4. 7 3. 3 4. 4. 3 4. 7 Hardness, DPN 296 324364 343 356 Warpage factor..- 023 0 063 087 TABLE VI 0-1080 Steel oo HonHot OD ETD 5.5% 177 r011 22% 22% +ETD +1216) Tensile strength, p.s.i--.144, 500 167, 000 178, 000 170, 500 168,500 Yield strength, p.s.l 76,000 129,000 151, 500 139, 000 135, 500 Elongation, percent 12. 5 5. 6. 45. 0 3. 6 lbs 16, 603 11, 450 12, 595 7, 443 Izod impact, ft. lbs 4. 73.0 4.0 3. 3 4. 7 Hardness, DPN- 296 330 304 7 350 350 Warpage factor;025 007 007 048 087 CD=Cold drawn at room temperature. ETD=Drawn at 800F.=l=50 F. Table V=Results air cooled. Table VI-- Results water or oilquench.

TABLE VH 4140 Steel oo Hon Hot OD ETD 5% 20% Roll 20% 20% +ETD +ETDTensile strength, p.s.i.-. 140, 000 165,000 189, 500 194, 250 211, 750Yield strength, p.s.l- 105, 750 182,000 189,000 188, 750 206, 000Elongation, percent--- 15. 9.0 9. 5 9.0 7. 0 Pull, lbs 18, 320 14, 88524, 045 14, 026 Izod impact, ft. lbs 9.0 4. 3 5. 3 2. 0 4. 0 Hardness,DPN... 307 336 394 378 402 Warpage factor 004 083 057 971 +1. 172

CD=Co1d drawn at room temperature. ETD=Drawn at 600 F.:l=25 F.

Table VII= Results air cooled.

Table VIII=Results water or oil quench.

TABLE XII C-1144 steel cold drawn to take a 21.6 percent reduction anddrawn at elevated temperature to take a 15.6 percent reduction followedby air coo g Tensile Yield Elonge- Warpage Tcmp. of draw, F. strength,strength, tlcn, factor p.s.i. p.s.l. Percent TABLE XIII C-1080 steelcold drawn to take a 5.5 percent reduction and drawn at elevatgdtemperature to take a 17.4 percent reduction followed by oil queue Thefollowing tables present data developed to show Tensile Yield Elongmwarpage the wide range of propertles which are secured by draw- Tempofdmw, o strength, strength, r n, factor ing at an elevated temperaturewithin the range described, Percent as compared to room temperature, butafter the steels 1 144, 500 76,000 12. 5 025 have first been giveneither a light or a heavy cold re 140,500 97,500 M +392 duction. 100,000 120, 000 4. a 055 883 129888 ti 1 182, 19 TABLE IX 100,000 183,0002.9 -.0s7 19288 132283 2'8 "823 (3-1018 steel cold drawn at roomtemperature to take an 8.2 percent reduction and drawn at elevatedtemperature to take an 18.0 percent 153'500 no'ooo reduction followed bywater quenching TABLE XIV Pull, Tensile Yield Warpage (3-1080 steel colddrawn to take a 22 percent reduction and drawn at Temp. of draw, F. lbs.etc. strength, strength, factor elevated temperature to take a 17percent reduction followed by air p.s.i. p.s.i. cooling 68,375 46,875+.021 Tensile Yield Elonga- Warpage 95, 000 92, 500 454 Temp. of draw,F. strength, strength, tlon, factor 95, 750 95. 000 p.s.i. p.s.i.Percent 124, 500 120, 000 116,500 113,000 112, 500 108, 750 169, 000133, 000 1. 4 341 95, 000 82, 500 178,000 144, 500 2. 1 350 750 79, 000183, 000 140, 000 3. 6 087 157, 000 126, 000 10. 0 044 TABLE X TABLE XVC4018 steel cold drawn at room temperature to take a 31.2 percentreduction and drawn at elevated temperature to take a 17.7 percentreduction followed by water quench Pull, Tensile Yield Werpage Temp. ofdraw, F. lbs. etc. strength, strength, factor p.s.i. p.s.i.

TABLE XI C-1l44 steel cold drawn to take a 4.6 percent reduction anddrawn at elevuelted temperature to take a. 17.7 percent reductionfollowed by air coo g 4140 steel cold drawn to take a 4.8 percentreduction and drawn at elevated temperature to take a 16.1 percentreduction followed by air coo mg Tensile Yield Elongo- Warpage Temp. ofdraw, F. strength, strength, tion, factor p.s.i. p.s.i. Percent TABLEXVI 4140 steel cold drawn to take a 20.3 percent reduction and drawn atelevated temperature to take a 17.7 percent reduction followed by aircooling Tensile Yield Elongu- Warpage Temp. of drew, F. strength,strength, tiou, factor p.s.i. p.s.i. Percent As illustrated by theforegoing data, steels having different mechanical and physicalproperties can be produced by the combination of steps which makes useof a cold reduction step in advance of taking a reduction at elevatedtemperature within the range of 200 F. to the lower critical temperaturefor the steel composition. From the standpoint of the strengthproperties of the steels, it will be apparent that for most of thesteels, the tensile strengths and yield strengths are maximized when thesteels, which have first been subjected to a cold reduction, aresubsequen y reduced when heated to a temperature within the range ofabout 400-900 F.

From the foregoing, it will be apparent that I have provided a processused in combination with the elevated temperature systems described andclaimed in the previously mentioned copending applications to improvethe physical and mechanical properties of steel. While I have discussedthe improvements as found in the increase in tensile and yield strength,others of the properties of the steels are also enhanced by thecombination of the steps which includes a cold reduction step in advanceof reduction at elevated temperature. These other properties includesurface finish, impact strength, machineability, pull load and the likephysical and mechanical properties.

As used herein and in the claims, the term bar is intended to includeand includes rounds, flats, tubing, wire, rod and the like steelssubjected to cold finishing operations. The term cold as used incombination with reduction is meant to relate to ambient temperaturesbut will include temperatures up to about 200 F.

It will be understood that changes may be made in the details of thechemistry of the steel, the amounts of reductions, and the means bywhich the reductions are carried out, without departing from the spiritof the invention, especially as defined in the following claims.

I claim:

1. The metallurgical process for the improvement of mechanical andphysical properties of steel of the nonaustenitic type having apearlitic structure in a matrix of free ferrite, consisting of thefollowing combination of steps in the order specified of extruding thesteel through an extrusion die to elfect reduction in cross-sectionalarea in a cold reduction step, and extruding the cold reduced steelthrough an extrusion die to eflect a further reduction incross-sectional area while the steel is at a temperature within therange of 200 F. to the lower critical temperature for the steelcomposition.

2. The metallurgical process for the improvement of mechanical andphysical properties of steel of the nonaustenitic type having apearlitic structure in a matrix of free ferrite, consisting of thefollowing combination of steps in the order specified of advancing thesteel through a die to effect reduction in cross-sectional area in acold reduction step, and, without any intermediate heat treatment,extruding the cold reduced steel through an extrusion die to effect afurther reduction in cross-sectional area while the steel is at atemperature within the range of 400900 F.

3. The metallurgical process for the improvement of mechanical andphysical properties of steel which steel strain hardens and whichhardens by some mode of precipitation when worked at a temperaturebetween 200 F. and the lower critical temperature of the steelcomposition, consisting of the following combination of steps in theorder specified of advancing the steel through a die to effect reductionin cross-sectional area in a cold reduction step, and, without anyintermediate heat treatment, advancing the cold reduced steel through adie to effect a further reduction in cross-sectional area while thesteel is heated to a temperature within the range of 200 F. to the lowercritical temperature for the steel composition.

4. The method as claimed in claim 3 which includes the additional stepof air cooling the steel after advancement through the die at elevatedtemperature.

5. The method as claimed in claim 3 which includes the additional stepof quenching the steel in a bath formed of a liquid selected from thegroup consisting of oil and water after advancement through the die atelevated temperature.

6. A steel product produced by the method of claim 3.

7. The metallurgical process for the improvement of mechanical andphysical properties of steel which strain hardens and which hardens bysome mode of precipitation when worked at a temperature between 400900=F., consisting of the following combination of steps in the orderspecified of advancing the steel through a die to effect a coldreduction in cross-sectional area, and, without any intermediate heattreatment, advancing the cold reduced steel through a die to effect afurther reduction in cross-sectional area while the steel is heated to atemperature within the range of 400-900 F.

8. The metallurgical process for the improvement of mechanical andphysical properties of steel which steel strain hardens and whichhardens by some mode of precipitation when worked at a temperaturebetween 400- 900 F. consisting of the following combination of steps inthe order specified of drawing the steel through a draw die in a coldreduction step to eifect reduction in crosssectional area, and, withoutany intermediate heat treatment, drawing the cold reduced steel througha draw die to effect a further reduction in cross-sectional area whilethe steel is heated to a temperature within the range of 400900 F.

9. The metallurgical process for the improvement of mechanical andphysical properties of steel which strain hardens and which hardens bysome mode of precipitation when worked at a temperature between 200 'F.and the lower critical temperature for the steel composition, consistingof the following combination of steps in the order specified ofadvancing the steel through a die to effect reduction in cross-sectionalarea in a cold reduction step, and, without any intermediate heattreatment, advancing the cold reduced steel through a draw die to effectreduction in cross-sectional area in a drawing operation while the steelis at a temperature within the range of 200 F. to the lower criticaltemperature for the steel composition.

10. The metallurgical process for the improvement of,

mechanical and physical properties of steel which strain hardens andwhich hardens by some mode of precipitation when worked at a temperaturebetween 200 F. and the lower critical temperature for the steelcomposition, consisting of the following combination of steps in theorder specified of advancing the steel through a die to effect reductionin cross-sectional area in a cold reduction step, and, without anyintermediate heat treatment, advancing the cold reduced steel through anextrusion die to effect reduction in cross-sectional area in anextrusion operation while the steel is at a temperature within the rangeof 200 F. to the lower critical temperature for the steel composition.

11. The metallurgical process for the improvement of mechanical andphysical properties of steel which strain hardens and which hardens bysome mode of precipitation when worked at a temperature between 200 F.and they lower critical temperature of the steel composition, consistingof the following combination of steps in the order specified of workingthe steel to effect a reduction in crosssectional area in a coldreduction step, and rolling the cold reduced steel to effect a furtherreduction in cross-sectional area in a rolling operation while the steelis at a temperature within the range of 200 F. to the lower criticaltemperature for the steel composition.

References Cited in the file of this patent

3. THE METALLURGICAL PROCESS FOR THE IMPROVEMENT OF MECHANICAL ANDPHYSICAL PROPERTIES OF STEEL WHICH STEEL STRAIN HARDENS AND WHICHHARDENS BY SOME MODE OF PRECIPITATION WHEN WORKED AT A TEMPERATUREBETWEEN 200*F. AND THE LOWER CRITICAL TEMPERATURE OF STELL COMPOSITION,CONSISTING OF THE FOLLOWING COMBINATION OF STEPS IN THE ORDER SPECIFIEDOF ADVANCING THE STEEL THROUGH A DIE TO EFFECT REDUCTION INCROSS-SECTIONAL AREA IN A COLD REDUCTION STEP, AND, WITHOUT ANYINTERMEDIATE HEAT TREATMENT, ADVANCING THE COLD REDUCED STEEL THROUGH ADIE TO EFFECT A FURTHER REDUCTION IN CROSS-SECTIONAL AREA WHILE THESTEEL IS HEATED TO A TEMPERATURE WITHIN THE RANGE OF 200*F. TO THE LOWERCRITICAL TEMPERATURE FOR THE STEEL COMPOSITION.